With technology development and continuing improvement in luminous efficacy, light emitting diodes (LEDs), as a new generation of lighting source, have been vastly used in backlight, display and decorative lighting, and have started to be used in home lighting and outdoor lighting. With LED applications continuing expanding, manufacturers are increasing their investment and R & D effort. On the other hand, due to fluctuations in fabrication processes or unstable and uncontrollable factors in fabrication equipment, it will sometimes happen that intact epitaxial wafers have to be scrapped which, however, contain substrates whose cost accounts for a considerable part of the cost of the epitaxial processes, in particular for large sized substrates developed nowadays. Presently, sapphire substrates have found increasing use in LED fabrication due to a variety of their advantages. For example, they have high mechanical strength and can be produced by well-established processes and used to make high-quality devices.
As the competition in the LED market becomes increasingly intense, there is a need to strip off the epitaxial surface portions of the intact wafers and recycle the sapphire substrates for reuse in order to reduce the production cost. Although intense research efforts have been made in the art, existing methods for sapphire recycling still more or less suffer from some problems such as high cost, high complexity and etc.
Chinese Patent Document CN104868020A discloses a method for sapphire substrate recycling, which includes first high-temperature baking, first rinsing, second high-temperature baking and second rinsing, of an epitaxial wafer, as well as optionally repeating these steps for N times. Since this method requires at least four steps involving repeated baking and rinsing processes, it is tedious and costly.